Beejive updated today, but with NO mention of being 4.0 compatible. I will have to check it out later though.
I never saw a Beejive update except for the 3.4 out a few days ago... and it didn't have multitasking or save state. AIM hasn't added it either. I hope they do soon because I use Beejive all the time to talk to my girl abroad in England and it would be nice to not have to wait for it to launch and load every time. I assume it will be out eventually. It took them 3 weeks to implement Push notifications after 3.0's launch.